What Causes Autism?

The exact cause of autism is not known, but research has pointed to several possible factors, including genetics (heredity), metabolic or neurological factors, certain types of infections, and problems occurring at birth.

Recent studies strongly suggest that some people have a genetic predisposition to autism, meaning that a susceptibility to develop the condition may be passed on from parents to children. Researchers are looking for clues about which genes contribute to this increased vulnerability. In some children, environmental factors may also play a role. Studies of people with autism have found abnormalities in several regions of the brain, which suggest that autism results from a disruption of early brain development while still developing in the mother's womb.

Other autism theories suggest:

The body's immune system may inappropriately produce antibodies that attack the brains of children, causing autism. This theory is not widely thought of as being valid.

Children with autism have abnormal timing of the growth of their brains. Early in childhood, the brains of children with autism grow faster and larger than those of normal children. Later, when normal children's brains get bigger and better organized, the brains of kids with autism grow more slowly.

Can Childhood Vaccines Cause Autism?

To date, there is no evidence that any vaccine can cause autism or any kind of behavioral disorder. A suspected link between the measles, mumps, rubella (MMR) vaccine and autism was suggested by some parents of children with autism, but well-documented, wide-ranging studies have discounted any association. One basis for the rejection of the theory is that typically, symptoms of autism are first noted by parents as their child begins to have difficulty with delays in speaking after age one. The MMR vaccine is first given to children at 12 to 15 months of age; autism cases with an apparent onset within a few weeks after the MMR vaccination may simply be an unrelated chance occurrence.

Speculation that a preservative used in vaccines, thimerosol, is responsible for an increase in autism cases has also led to studies that have shown no evidence of a link.